Instrument for air ionization

ABSTRACT

An air ionizer is provided of the type in which a corona discharge is produced at the point of a sharp `needle` by connecting it to a source of high potential. One or more needles, mounted in an insulator, point in a direction opposite to the eventual flow of air ions. At ions emitted from the point of the needle are reflected by a reflector. The reflector may comprise a sheet of insulating material or an electrically conductive material, e.g. a metal, mounted on insulators. The reflector may be provided with perforations for the passage of air therethrough such that the ionizer may, with advantage, be placed in a moving air stream. The insulator on which the needle(s) is or are mounted may comprise a polythene cable or a printed circuit board.

This invention relates to air ionizers of the type in which a coronadischarge is produced at the point of a sharp `needle` by connecting itto a source of high potential, typically 3000 to 6000 volts. The coronagives rise to a stream of electrically charged air molecules, or ions,the sign of which corresponds to the sign of the potential applied tothe `needle.` The ions are propelled into the surrounding air by thewell known `electric wind` effect.

It is usual in such ionizers for the `needle` to be mounted so that thestream of ionized air leaving its point flows directly into the adjacentair-space for breathing. The needle is therefore pointing towards thepatient or other recipient and, unless protected, can be dangerousmechanically, as a sharp point, and in some cases electrically, becauseof its high potential. It is of course usual to incorporate a currentlimiting device in the electrical supply to the needle, but sensitivepeople can sometimes find electrical contact with the needle disturbing.Since anything in the nature of a protective grill placed over theneedle will completely stop the flow of ions, it is usual in suchinstruments for the needle(s) to remain largely unprotected.

The object of the present invention is to provide full protection forthe `needle,` or `needles,` whilst still retaining an unimpeded flow ofair ions.

According to the present invention, in a first aspect thereof, aninstrument for air ionization comprises a needle mounted in aninsulator, the needle, in operation of the instrument, being connectedto a source of high potential, and being directed towards an air ionreflector, in a direction opposite to that in which the eventual flow ofair ions is required.

The air ion reflector may comprise a sheet of insulating material.Alternatively the air ion reflector may be made of an electricallyconductive material, preferably a metal, and mounted on insulatingmeans.

Desirably the air ion reflector has perforations to permit the passageof air therethrough.

An instrument embodying the invention, and modifications thereof, willnow be described, by way of example only, with reference to theaccompanying diagrammatic drawings, in which:

FIG. 1 is a side view of the said instrument;

FIG. 2 is a perspective view of a first said modification;

FIG. 3 shows a bias circuit for use with the said instrument;

FIGS. 4 to 6 illustrate a second said modification;

FIG. 7 shows an indicator for use with the said instrument;

FIGS. 8 to 11 illustrate a third said modification; and

FIGS. 12 and 13 show respectively sectional and perspective views of afourth said modification.

Referring first to FIG. 1. A `needle` 1, mounted in an insulator 2, andconnected to a suitable source of high potential E, is directed towardsan air ion reflector in the form of a plate 3 in a direction opposite tothat in which the eventual flow of air ions is required. The point ofthe needle is therefore directed away from the user so that the risk ofinjury by accidental contact direct from the front is removed. Air ionsemitted at the needle tip impinge on the plate 3 and a surface charge ofstatic electricity, having the same sign as that of the ions, isestablished. A state of equilibrium is quickly reached in which only asmall number of ions, sufficient to compensate for any leakage from thesurface, continue to reach plate 3, the vast majority being deflectedback in the opposite direction by virtue of the repulsion effect of theelectrostatic field created by the charged surface. The plate 3therefore acts as an electrostatic reflector or `mirror,` enabling theair ions to be deflected in a direction substantially opposite to thatin which the needle is pointing. The plate 3 may comprise a sheet ofinsulating material, or alternatively it may comprise a conductivematerial, such as a metal, mounted on suitable insulating means (notshown).

In practice, the electrostatic charge laid down on plate 3 and oninsulator 2, being of the same sign and of comparable potential to thatof needle 1, operate to reduce the field strength at the needle tip tobelow that at which the corona discharge can be maintained. With aneedle in free space the necessary field exists by virtue of thedifference in potential between the needle and its surroundings, or`earth`. The necessary field is therefore restored by introducing one ormore conductive plates 5 (FIG. 2) in suitable proximity to the needletip, plates 5 being held at earth or other suitable potential. Oneconsequence of this is that an ion current Ip flows from the needle tipto plates 5. Under some conditions current Ip can reach a magnitude suchthat unacceptable amounts of ozone are produced. As a further feature ofthis invention, current Ip is controlled at an acceptable value byapplying a suitable bias potential V, of the same sign as potential E toplates 5. This bias potential can be derived from an external source, ordeveloped automatically from a self regulating bias circuit consistingof a very high value resistor R connected between plates 5 and earth(FIG. 3). This function is best performed by making use of the reversevoltage characteristics of a small silicon high voltage rectifier whichmeets the necessary requirements of very small leakage current and highoperating voltage. In addition, the onset of the avalanche conditionserves to limit the maximum potential which can be acquired by plates 5under fault conditions. The potential developed across resistor, orrectifier R, finds an equilibrium point when it reaches a value at whichthe ion current drawn is just sufficient to maintain it. This followsfrom the fact that the ion current Ip, falls off as the plate biaspotential V rises. The circuit therefore provides an automatic controlof plate bias and therefore of ozone level, the operating point beingdetermined by the choice of the resistor or rectifier R.

FIGS. 4 to 6 illustrate one practical modification of the invention. Theinsulator 2, in FIG. 2, is replaced by a length of polythene insulatedcable 2A, the needle, or needles 1, being pushed through the insulationso as to contact the central wire 6, as shown in FIG. 4. Plates 5 can,for example, take the form of foil or other conductive wrappings roundthe polythene insulation. This assembly may then be mounted in a simpleplastics extrusion 7 (FIG. 5) which may then be mounted over plate 3(FIG. 6) on members or pillars 10. Connection to the needles, viaconductor 6 in cable 2A, is effected via one mounting screw 9, and thatto the plates 5, via the other mounting screw 9. By keeping the spacingbetween extrusion 7 and insulator panel 3 small, the needles 1, arefully protected.

The underside of plate 3 may be used for mounting the electricalcomponents of the high potential supply circuit providing the probepotentials E and, where required, bias potential V. When necessary thiscan take the form of a printed circuit board. The complete assembly maythen be mounted in a box, or as required.

The small current Ip collected by the plates 5, or their equivalents onan alternative printed circuit assembly, can be used to operate anindicator consisting of a small neon lamp N and capacitor C (FIG. 7) andpreferably a ballast resistor R. In operation, the current Ip serves tocharge the capacitor C to a potential sufficient to trigger the neonlamp N, whereupon the capacitor is discharged through the neon lamp,which then ceases to conduct. The capacitor C then charges again and thecycle is repeated. The rate at which the neon lamp flashes is a measureof current Ip, and therefore of the efficiency of the circuit operation.

A further practical modification of the invention is illustrated inFIGS. 8 to 11 where a printed circuit board is used instead of thepolythene cable referred to in FIG. 4.

In this modification, a printed circuit board of known type 12, havingconductive foil on both surfaces is etched on one surface (FIG. 9) toproduce the required number of plates 5, all interconnected and beingsuitably spaced to allow needles 1 to be mounted in holes drilled in theinsulating board between them. On the other side of the board (FIG. 10)the conductive foil is etched away so as to leave a thin conductivestrip 13 having pads 14 to which the undersides of the needle aresoldered, and pad 15 for connection to the supply. The needle pointstherefore project upwards between the plates 5, as in side elevationFIG. 8. The complete strip may be mounted in a suitable moulded housing16, as shown in FIG. 11 and again mounted, for example, in the mannershown in FIG. 6. The surface of the plate 3, may in either case be flatas illustrated or alternatively it can be curved in a convex or concavemanner to give a preferred distribution of the reflected ions.

FIGS. 12 and 13 provide for applications in which it is required tomount the ionizer instrument in a moving air stream for the purpose ofionizing the air flowing past it. For example, it may be required toionize the air emerging from a ventilation or heating duct into a livingroom, office or other space.

In such a case, the plate 3 may present an obstruction to the movingair, thus preventing it from passing effectively through the ionizationarea between the said plate and the needle assembly. In the presentinvention this limitation is overcome by constructing the plate 3 from asuitable material having perforations through which the moving air canpass. These can take any suitable form, such as closely spaced holes orslots, or the material can take the form or wire or metal mesh mountedon suitable insulators.

A needle assembly, making use of a printed circuit board 12 (FIG. 12),is mounted in a suitably moulded housing 16. Such an assembly may haveany required number of needles 1, consistent with the total length ofthe assembly. As shown in FIG. 13, the assembly is then mounted on twomembers 10, secured to a rectangular frame, 17, in such a way that theneedles are facing towards the frame. In the illustration a wire mesh,constituting the plate 3 is mounted in frame, 17, the frame itself orsuitable inserts, serving to insulate the mesh electrically. Thecomplete assembly is then mounted over a ventilating or heating duct,terminating in a conventional grill fitting 18. Air emerging from thegrill therefore passes through the mesh 3, and thus through the ionizingarea, as indicated by the arrows 19.

The design of the ionizer and reflector assembly can, of course, beadapted to conform to any size or shape of duct or grill, and more thanone housing 16 containing ionizing means may be employed. Again, theionizer/reflector assembly may be designed to fit in front of a fan, orblower unit instead of a duct, or it may be mounted over a heater,radiator, or similar device producing a moving current of air. The unitmay be designed to fit over a window vent through which air is drawn byan extractor fan mounted elsewhere.

I claim:
 1. An instrument for air ionization comprising a needle mountedin an insulator .Iadd.and having a pointed end, .Iaddend.and an air ionreflector, the needle, in operation of the instrument, being connectedto a source of high potential, and .Iadd.the needle point .Iaddend.beingdirected towards said air ion reflector, in a direction opposite to thatin which the eventual flow of air ions is required.
 2. An instrumentaccording to claim 1, wherein said air ion reflector comprises a sheetof insulating material.
 3. An instrument according to claim 1, whereinsaid air ion reflector comprises an electrically conductive material,mounted on insulating means.
 4. An instrument according to claim 3,wherein said electrically conductive material is a metal.
 5. Aninstrument according to claim 1, wherein said air ion reflector hasperforations for the passage of air therethrough.
 6. An instrumentaccording to claim 1, wherein at least one conductive plate is placed inproximity to the point of said needle.
 7. An instrument according toclaim 6, wherein a bias circuit is connected between said at least oneconductive plate and earth.
 8. An instrument according to claim 6,further comprising an indicator for indicating the efficiency ofoperation in use of the said instrument, wherein said at least oneconductive plate is connected to said indicator.
 9. An instrumentaccording to claim 1, wherein said insulator comprises a polythenecable.
 10. An instrument according to claim 1, wherein said insulatorcomprises a printed circuit board.